Methods of identifying inhibitors of GTP cyclohydrolase I and II

ABSTRACT

The present invention relates to the identification of fungal GTP cyclohydrolase II as a target for fungicides, to a method for identifying antifungal agents based on fungal GTP cyclohydrolase II, and also to the use of compounds identified as fungicides via the abovementioned method.

This application is a divisional of application Ser. No. 10/526,207,filed Mar. 4, 2005, now abandoned, which is the National Stage ofInternational Application No. PCT/EP2003/009369, filed Aug. 23, 2003,which claims priority to European Patent Application No. 02020051.5,filed on Sep. 6, 2002. The entire contents of these applications arehereby incorporated by reference herein.

The present invention relates to the identification of fungal GTPcyclohydrolase II as a target for fungicides, to a method foridentifying antifungal agents based on fungal GTP cyclohydrolase II, andalso to the use of compounds identified as fungicides via theabovementioned method.

The basic principle of identifying fungicides via inhibition of adefined enzyme is known (WO 00/3657). With regard to the increasingproblems regarding resistance to fungicides, however, there exists agreat need for detecting enzymes which might constitute novel targetsfor fungicides.

In practice, the detection of targets is extremely difficult, sinceoften the inhibition of an enzyme participating in a biochemical pathwaydoes not lead to decreased growth or infectivity of the pathogenicfungi. A putative reason is the existence of an alternative, maybeunknown pathway used by the fungus. Thus, even if the function of thegene itself is known, it is not possible to predict a fitness for use asa fungicide target.

Thus, it is an object of the present invention to identify a novelfungicide target.

Surprisingly, we have found that fungal GTP cyclohydrolase is suitableas a fungicide target. The present invention comprises the use of afungal GTP cyclohydrolase as target for the identification of antifungalagents and methods of identifying antifungal agents which inhibit fungalGTP cyclohydrolase II comprising the following steps:

-   -   i. incubating, with at least one candidate compound, a fungal        GTP cyclohydrolase II under conditions allowing the binding of        the candidate compound to the fungal GTP cyclohydrolase II        polypeptide; and    -   ii. selecting, by step ii), at least one candidate compound        which binds to the fungal GTP cyclohydrolase II of step i); or    -   iii. selecting, by step iii), at least one candidate compound        which reduces or blocks the activity of the fungal GTP        cyclohydrolase II of step i); or    -   iv. selecting, by step iv), at least a candidate compound which        inhibits or decreases transcription, translation or expression        of the fungal GTP cyclohydrolase II of step i).

Some of the terms used in the description are defined at this point.

“Affinity tag”: this denotes a peptide or polypeptide whose codingnucleic acid sequence can be fused to the sequence encoding the fungalGTP cyclohydrolase II, either directly or using a linker, by customarycloning techniques. The affinity tag serves to isolate the recombinantfungal GTP cyclohydrolase II by means of affinity chromatography. Theabovementioned linker can optionally comprise a protease cleavage site(for example for thrombin or factor Xa), whereby the affinity tag can becleaved off from the fungal GTP cyclohydrolase II, as required. Examplesof customary affinity tags are the “his-tag”, for example from Quiagen,Hilden, “strep-tag”, “myc-tag” (Invitrogen, Carlsberg), New EnglandBiolab's tag which consists of a chitin-binding domain and an intein,and what is known as the CBD-tag from Novagen.

“Antifungal agents” are agents against pathogenic fungi such as humanand plant pathogens, preferably plant pathogens.

“Enzymatic activity/activity assay”: the term enzymatic activitydescribes the ability of an enzyme to convert a substrate into aproduct. In this context, both the natural substrate of the enzyme and asynthetic modified analog of the natural substrate can be used. Theenzymatic activity can be determined in what is known as an activityassay via the increase in the product, the decrease in the startingmaterial, the decrease or increase in a specific cofactor, or acombination of at least two of the aforementioned parameters as afunction of a defined period of time. If the enzyme catalyzes areversible reaction, both the starting material and the product may beemployed as substrate in the activity assay in question.

“Expression cassette or nucleic acid sequence”: an expression cassettecomprising a nucleic acid sequence according to the inventionoperatively linked to a promotor and/or terminator sequence isunderstood as meaning, for example, a genomic or a complementary DNAsequence or an RNA sequence and semisynthetic or fully synthetic analogsof these. These sequences may be present in linear or circular form,extrachromosomally or integrated into the genome. The nucleic acidsequences according to the invention can be generated synthetically orobtained naturally or comprise a mixture of synthetic and natural DNAcomponents, and be composed of a variety of heterologous gene segmentsof various organisms.

Artificial nucleic acid sequences too are suitable in this context aslong as they make possible the expression of the fungal GTPcyclohydrolase II in a cell or an organism. For example, syntheticnucleotide sequences can be generated which were optimized with regardto the codon usage of the organisms to be transformed.

All of the abovementioned nucleotide sequences can be generated in amanner known per se by chemical synthesis from the nucleotide units suchas, for example, by fragment condensation of individual overlappingcomplementary nucleotide units of the double helix. Oligonucleotides canbe synthesized chemically for example in a known manner using thephosphoamidite method (Voet, Voet, 2nd Edition, Wiley Press New York,pages 896-897). When preparing an expression cassette, a variety of DNAfragments can be manipulated to give rise to a nucleotide sequence whichreads in the correct direction and is in-frame. The nucleic acidfragments are linked to each other by general cloning techniques as aredescribed, for example in T. Maniatis, E. F. Fritsch and J. Sambrook,Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory,Cold Spring Harbor, N.Y. (1989) and in T. J. Silhavy, M. L. Berman andL. W. Enquist, Experiments with Gene Fusions, Cold Spring HarborLaboratory, Cold Spring Harbor, N.Y. (1984) and in Ausubel, F. M. etal., Current Protocols in Molecular Biology, Greene Publishing Assoc.and Wiley-Interscience (1994).

“Gene” describes a nucleic acid sequence which encodes a protein andwhich can be transcribed into RNA (mRNA, rRNA, tRNA, snRNA, sense RNA orantisense RNA) and which can optionally be associated with regulatorysequences. Examples of regulatory sequences are promoter sequences.Other elements which are optionally present are, for example, introns.

“Genetic control sequence”: the term of the genetic control sequences(which is equivalent to the term “regulatory sequence”) describessequences which have an effect on the materialization or the function ofthe expression cassette according to the invention and which ensure forexample transcription and, if appropriate, translation in prokaryotic oreukaryotic organisms. Examples are promoters or what are known asenhancer sequences. In addition to these control sequences, or insteadof these sequences, the natural regulation of these sequences before theactual structural genes may still be present and, if appropriate, mayhave been modified genetically in such a way that the natural regulationhas been inactivated and the expression of the fungal GTP cyclohydrolaseII gene increased. The choice of the control sequence depends on thehost organism or starting organism. Genetic control sequencesfurthermore also encompass the 5′-untranslated region, introns or thenoncoding 3′-region of genes. Control sequences are furthermoreunderstood as being those which make possible a homologous recombinationor insertion into the genome of a host organism or which permit theremoval from the genome.

“Functional equivalents” in the present context describe nucleic acidsequences which hybridize under standard conditions with the nucleicacid sequence encoding the GTP cyclohydrolase II or portions of thenucleic acid sequence encoding the GTP cyclohydrolase II, and which arecapable of bringing about the expression of an enzymatically activefungal GTP cyclohydrolase II in a cell or an organism.

It is advantageous to use short oligonucleotides of a length between 10to 50 bp, preferably 15-40 bp, for example of the conserved or otherregions, which can be determined via comparisons with other relatedgenes in a manner known to the skilled worker for the hybridization.Alternatively, it is also possible to use longer fragments of thenucleic acids according to the invention or the complete sequences forthe hybridization. These standard conditions vary depending on thenucleic acid used, viz. oligonucleotide, longer fragment or completesequence, or depending on which type of nucleic acid, viz. DNA or RNA,is being used for the hybridization. Thus, for example, the meltingtemperatures for DNA:DNA hybrids are approx. 10° C. lower than those ofDNA:RNA hybrids of equal length.

Standard conditions are understood as meaning, depending on the nucleicacid, for example temperatures between 42 and 58° C. in an aqueousbuffer solution with a concentration of between 0.1 and 5×SSC(1×SSC=0.15 M NaCl, 15 mM sodium citrate, pH 7.2) or additionally in thepresence of 50% formamide such as, for example, 42° C. in 5×SSC, 50%formamide. The hybridization conditions for DNA:DNA hybrids areadvantageously 0.1×SSC and temperatures of between approximately 20° C.and 45° C., preferably between approximately 30° C. and 45° C. Thehybridization conditions for DNA:RNA hybrids are advantageously 0.1×SSCand temperatures of between approximately 30° C. and 55° C., preferablybetween approximately 45° C. and 55° C. These temperatures stated forthe hybridization are melting temperature values which have beencalculated by way of example for a nucleic acid with a length of approx.100 nucleotides and a G+C content of 50% in the absence of formamide.The experimental conditions for DNA hybridization are described inspecialist textbooks of genetics such as, for example, Sambrook et al.,“Molecular Cloning”, Cold Spring Harbor Laboratory, 1989 and can becalculated using formulae known to the skilled worker, for example as afunction of the length of the nucleic acids, the type of the hybrids orthe G+C content. The skilled worker can find more information onhybridization in the following textbooks: Ausubel et al. (eds), 1985,Current Protocols in Molecular Biology, John Wiley & Sons, New York;Hames and Higgins (eds), 1985, Nucleic Acids Hybridization: A PracticalApproach, IRL Press at Oxford University Press, Oxford; Brown (ed),1991, Essential Molecular Biology: A Practical Approach, IRL Press atOxford University Press, Oxford.

A functional equivalent is furthermore also understood as meaning, inparticular, natural or artificial mutations of the relevant nucleic acidsequences of the fungal GTP cyclohydrolase II and their homologs fromother organisms which make possible the expression of the enzymaticallyactive fungal GTP cyclohydrolase II in a cell or an organism.

Thus, the scope of the present invention also extends to, for example,those nucleotide sequences which are obtained by modification of thenucleic acid sequence of a GTP cyclohydrolase II. The purpose of such amodification can be, for example, the insertion of further cleavagesites for restriction enzymes, the removal of excess DNA, or theaddition of further sequences. Proteins which are encoded via saidnucleic acid sequences should still maintain the desired functions,despite the deviating nucleic acid sequence.

The term functional equivalent may also refer to the protein encoded bythe nucleic acid sequence in question. In this case, the term functionalequivalent describes a protein whose amino acid sequence is up to aspecific percentage homologous to or identical with that of the GTPcyclohydrolase II.

Functional equivalents thus encompass naturally occurring variants ofthe sequences described herein, and also artificial, for examplechemically synthesized, nucleic acid sequences adapted to the codonusage, or the amino acid sequences derived therefrom.

In general, it can be said that functional equivalents independently ofthe amino acid sequence in question (encoded by a corresponding nucleicacid sequence) have in each case the enzymatic activity of a GTPcyclohydrolase II.

“GTP cyclohydrolase II activity” denotes the ability of an enzyme tocatalyse a reaction, wherein GTP is metabolized into2,5-diamino-6-ribosylamino-4(H)-pyrimidinone 5′-monophosphate,pyrophosphoric acid and formic acid.

“Homology” between two nucleic acid sequences or polypeptide sequencesis defined by the identity of the nucleic acid sequence/polypeptidesequence by in each case the entire sequence length, which is calculatedby alignment with the aid of the program algorithm GAP (WisconsinPackage Version 10.0, University of Wisconsin, Genetics Computer Group(GCG), Madison, USA), setting the following parameters:

Gap weight: 8 Length weight: 2 Average match: 2,912 Average mismatch:−2,003 matrix BLOSUM 62

The term “homology” is used herein as a synonym for “identity”.

“Mutations” comprise substitutions, additions, deletions, inversions orinsertions of one or more nucleotide residues, which may also lead to amodification of the corresponding amino acid sequence of the fungal GTPcyclohydrolase II by substitution, insertion or deletion of one or moreamino acids.

“Knock-out transformant” refers to a transgenic organism, in which aspecific gene has been inactivated in a directed fashion by means oftransformation.

“Natural genetic environment” is understood as meaning the naturalchromosomal locus in the organism of origin or the presence in a genomiclibrary. In the case of a genomic library, the natural geneticenvironment of the nucleic acid sequence is preferably retained at leastin part. The environment flanks the nucleic acid sequence at least onthe 5′ or 3′ side and has a sequence length of at least 50 bp,preferably at least 100 bp, especially preferably at least 500 bp, veryespecially preferably at least 1000 bp, most preferably at least 5000bp.

“Operative linkage”: An operative or else functional linkage isunderstood as meaning the sequential arrangement of promoter, codingsequence, terminator and, if appropriate, further regulatory elements insuch a way that each of the regulatory elements can, upon expression ofthe coding sequence, fulfil its function as intended.

“Recombinant DNA” describes a combination of DNA sequences in anarrangement other than their natural arrangement, which can be generatedby recombinant DNA technology, but also DNA comprising the endogenousand foreign or synthetic DNA, also homologous and heterologous DNA basedon the relatedness of the organisms.

“Recombinant DNA technology”: generally known techniques from fusing DNAsequences (for example described in Sambrook et al., 1989, Cold SpringHarbor, N.Y., Cold Spring Harbor Laboratory Press).

“Origins of replication” ensure the amplification of the expressioncassettes or vectors according to the invention in microorganisms, forexample pBR322 ori or P15A ori in E. coli (Sambrook et al: MolecularCloning. A Laboratory Manual, 2nd ed. Cold Spring Harbor LaboratoryPress, Cold Spring Harbor, N.Y., 1989).

“Reporter genes” encode readily quantifiable proteins. Using thesegenes, an assessment of transformation efficacy or of the site or timeof expression can be made via growth, fluorescence, chemoluminescence,bioluminescence or resistance assay or via photometric measurement(intrinsic color) or enzyme activity. Very especially preferred in thiscontext are reporter proteins (Schenborn E, Groskreutz D. Mol.Biotechnol. 1999; 13(1):29-44) such as the “green fluorescence protein”(GFP) (Gerdes H H and Kaether C, FEBS Lett. 1996; 389(1):44-47; Chui W Let al., Curr. Biol. 1996, 6:325-330; Leffel S M et al., Biotechniques.23(5):912-8, 1997), chloramphenicol acetyl transferase, a luciferase(Giacomin, Plant Sci. 1996, 116:59-72; Scikantha, J. Bact. 1996,178:121; Millar et al., Plant Mol. Biol. Rep. 1992 10:324-414), andluciferase genes, in general β-galactosidase or β-glucuronidase(Jefferson et al., EMBO J. 1987, 6, 3901-3907), the Ura3 gene, the Ilv2gene, the 2-desoxyglucose-6-phosphate phosphatase gene, β-lactamasegene, the neomycin phosphotransferase gene, the hygromycinphosphotransferase gene, or the BASTA (=gluphosinate) resistance gene.

“Selection markers” impart resistance to antibiotics. Examples which maybe mentioned are the neomycin-phosphotransferase-gen gene, which impartsresistance to the aminoglyciside antibiotics neomycin (G 418), kanamycinand paromycin (Deshayes A et al., EMBO J. 4 (1985) 2731-2737), the sulgene (Guerineau F et al., Plant Mol. Biol. 1990; 15(1):127-136), thehygromycin B phosphotransferase-Gen (Gen Bank Accession NO: K 01193) andthe she-ble gene, which imparts resistance to the bleomycin antibioticzeocin. Other examples of selection marker genes are genes which impartresistance to 2-desoxyglucose-6-phosphate (WO 98/45456) orphosphinothricin and the like, or those which impart resistance toantimetabolites, for example the dhfr gene (Reiss, Plant Physiol. (LifeSci. Adv.) 13 (1994) 142-149). Also suitable are genes such as trpB orhisD (Hartman S C and Mulligan R C, Proc. Natl. Acad. Sci. USA. 85(1988) 8047-8051). Also suitable are the mannose-phosphate isomerasegene (WO 94/20627), the ODC (ornithin decarboxylase) gene (McConlogue,1987 in: Current Communications in Molecular Biology, Cold Spring HarborLaboratory, Ed.), or the Aspergillus terreus deaminase (Tamura K et al.,Biosci. Biotechnol. Biochem. 59 (1995) 2336-2338).

“Significant decrease”: referring to the enzymatic activity, isunderstood as meaning the decrease in the enzymatic activity of theenzyme incubated with a candidate compound in comparison with theactivity of an enzyme not incubated with the candidate compound, whichlies outside an error in measurement.

“Substrate”: Substrate is the compound which is recognized by the enzymein its original function and which is converted into a product by meansof a reaction catalyzed by the enzyme.

“Transgenic”: Referring to a nucleic acid sequence, an expressioncassette or a vector comprising said nucleic acid sequence or anorganism transformed with said nucleic acid sequence, expressioncassette or vector, transgenic describes all those constructionsgenerated by recombinant methods in which either the nucleic acidsequence of the fungal GTP cyclohydrolase II or a genetic controlsequence linked operably to the nucleic acid sequence of the fungal GTPcyclohydrolase II or a combination of both of the aforementioned nucleicacid sequences.

GTP cyclohydrolase II catalyses the first step in the biosynthesis ofriboflavin (vitamin B2), wherein GTP is metabolized into2,5-diamino-6-ribosylamino-4(H)-pyrimidinone 5′-monophosphate,pyrophosphoric acid and formic acid (Ritz et. al. JBC 2001, 276:22273-22277). GTP cyclohydrolase II can be used for fermetativeriboflavin synthesis in Ashbya gossypii (WO 95/26406).

In plants, GTP cyclohydrolase II is used as a target for herbicides (WO00/40744). The plant enzyme, however, differs significantly from thefungal enzyme. The identity between fungal GTP cyclohydrolase II fromAshbya gossypii (SEQ ID NO:2) and plant GTP cyclohydrolase II fromArabidopsis thaliana (SWISS-PROT P47924) is only 31%. The identitybetween bacterial GTP cyclohydrolase II from Escherichia coli(SWISS-PROT P25523) and SEQ ID NO:2 is 48%.

Experiments in the yeast Saccharomyces cerevisiae indicate that GTPcyclohydrolase II is not essential for yeast (Saccharomyces GenomDatabase (SGD); http://genome-www.stanford.edu/Saccharomyces see forhttp://genome-www4.stanford.edu/cgi-bin/SGD/phenotype/phenotype.pl?feat=RIB1&type=locus.

Surprisingly, it was found that GTP cyclohydrolase II is a suitablefungicide target by demonstrating the essential role of GTPcyclohydrolase II for the pathogenic filamentous fungi Ashbya gossypii.The present invention therefore provides methods of using a fungal GTPcyclohydrolase II polypeptide (used herein synonymous to fungal GTPcyclohydrolase II) encoding nucleic acid sequenence to identifyinhibtors thereof, which then can be used as fungicides to suppress thegrowth of pathogenic fungi.

The term “pathogenic fungi” denotes fungi which colonize a host (a plantor a mammal) and cause disease, e.g. human pathogenens selected from thegroup consisting of the genera and species Candida such as Candidaalbicans, Candia stettatoidea, Candiala tropicatis, Candidaparapsilosis, Candida krusei, Candida pseudotropicatis, Candidaquittermondii, Candida rugosa, Aspergillus such as Aspergillusfumigatus, Aspergillus flavus, Aspergillus niger, Aspergillus nidulans,Aspergillus terreus, Rhizopus such as Rhizopus arrhizus, Rhizopusoryzae, Absidia such as Absidia corymbifera, Absidia ramosa and Mucorsuch as Mucor pusiltus or phytopathogenic filamentous fungi selectedfrom the group consisting of the genera and species Ashbya such asAshbya gossypii, Alternaria, Podosphaera, Sclerotinia, Physalospora suchas Physalospora canker, Botrytis species such as Botrytis cinerea,Corynespora such as Corynespora melonis; Colletotrichum; Diplocarponsuch as Diplocarpon rosae; Elsinoe such as Elsinoe fawcetti, Diaporthesuch as Diaporthe citri; Sphaerotheca; Cinula such as Cinula neccata,Cercospora; Erysiphe such as Erysiphe cichoracearum and Erysiphegraminis; Sphaerotheca such as Sphaerotheca fuliginea; Leveillula suchas Leveillula taurica; Magnaporte species such as Magnaporthe (M.)grisea, Mycosphaerella; Phyllactinia such as Phyllactinia kakicola;Gloesporium such as Gloesporium kaki; Gymnosporangium such asGymnosporangium yamadae, Leptotthrydium such as Leptotthrydium pomi,Podosphaera such as Podosphaera leucotricha; Pyrenophora (P.) such as P.graminea, P. hordei, P. japonica, P. teres, P. teres f. maculata, P.teres f. teres, P. tritici-repentis, Gloedes such as Gloedes pomigena;Cladosporium such as Cladosporium carpophilum; Phomopsis; Phytopora;Phytophthora such as Phytophthora infestans; Verticillium; Glomerellasuch as Glomerella cingulata; Drechslera; Bipolaris; Personospora;Phaeoisariopsis such as Phaeoisariopsis vitis; Spaceloma such asSpaceloma ampelina; Pseudocercosporella such as Pseudocercosporellaherpotrichoides; Pseudoperonospora; Puccinia; Typhula; Pyricularia suchas Pyricularia oryzae; Rhizoctonia; Stachosporium such as Stachosporiumnodorum; Uncinula such as Uncinula necator; Ustilago such as Ustilagomaydis; Gaeumannomyces species such as Gaeumannomyces graminis andFusarium (F.) such as F. dimerium, F. merismoides, F. lateritium, F.decemcellulare, F. poae, F. tricinctum, F. sporotrichioides, F.chlamydosporum, F. moniliforme, F. proliferatum, F. anthophilum, F.subglutinans, F. nygamai, F. oxysporum, F. solani, F. culmorum, F.sambucinum, F. crookwellense, F. avenaceum ssp. avenaceum, F. avenaceumssp. aywerte, F. avenaceum ssp. nurragi, F. hetrosporum, F. acuminatumssp. acuminatum, F. aduminatum ssp. armeniacum, F. longipes, F.compactum, F. equiseti, F. scripi, F. polyphialidicum, F. semitectum andF. beomiforme, preferably, the term “pathogenic fungi” denotesfilamentous phytopathogenic fungi mentioned above.

In one embodiment, the present invention encompasses a method foridentifying antifungal agents comprising the following steps:

-   -   i. incubating, with at least one candidate compound, a fungal        GTP cyclohydrolase II under conditions allowing the binding of        the candidate compound to the fungal GTP cyclohydrolase II; and    -   ii. selecting, by step ii), at least one candidate compound        which binds to the fungal GTP cyclohydrolase II of step i); or    -   iii. selecting, by step iii), at least one candidate compound        which reduces or blocks the activity of the fungal GTP        cyclohydrolase II of step i); or    -   iv. selecting, by step iv), at least a candidate compound which        inhibits or decreases transcription, translation or expression        of the fungal GTP cyclohydrolase II.

Preferably, the fungal GTP cyclohydrolase II is encoded by a nucleicacid sequence comprising

-   -   a) a nucleic acid sequence shown in SEQ ID NO:1; or    -   b) a nucleic acid sequence which, owing to the degeneracy of the        genetic code, can be deduced from the amino acid sequence shown        in SEQ ID NO: 2 by back translation; or    -   c) a nucleic acid sequence which, owing to the degeneracy of the        genetic code, can be deduced from a functional equivalent of the        amino acid sequence shown in SEQ ID NO: 2, which has an identity        with SEQ ID NO:2 of at least 49%, by back translation.

The functional equivalent of SEQ. ID NO:2 set forth in c) has anidentity of at least 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%preferably at least 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%,68%, 69%, and 70% more preferably 71%, 72%, 73%, 74%, 75%, 76%, 77%,78%, 79%, 80%, 81%, 82%, 83%, 84%, 85% most preferably at least 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% homologywith the SEQ ID NO:2.

The nucleic acid sequence originates from a fungus, wherein the termfungus denotes the above-mentioned pathogenic fungi and yeast such asSaccharomyces species (e.g. S. cerevisiae), Pichia species (e.g. P.pastoris, P. methanolica), Schizosaccharomyces species (e.g.Schizosaccharomyces pombe) and Klyveromyces species (e.g. K. lactis)

Within the scope of the present invention also novel nucleic acidsequences encoding a fungal GTP cyclohydrolase are provided, wherebysaid nucleic acid sequences comprise

-   -   a) a nucleic acid sequence shown in SEQ ID NO:4; or    -   b) a nucleic acid sequence which, owing to the degeneracy of the        genetic code, can be deduced from the amino acid sequence shown        in SEQ ID NO:5 by back translation; or    -   c) a nucleic acid sequence which, owing to the degeneracy of the        genetic code, can be deduced from a functional equivalent of the        amino acid sequence shown in SEQ ID NO:5, which has an identity        with SEQ ID NO:5 of at least 66%, by back translation.

The functional equivalent of SEQ ID NO:4 set forth in c) has an identityof at least 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%,preferably at least 77%, 78%, 79%, 80%, 81%, 82%, 83%, more preferably84%, 85%, 86%, 87%, 88%, 89%, 90%, 91% most preferably at least 92%,93%, 94%, 95%, 96%, 97%, 98%, 99% homology with the SEQ ID NO:5.

The selection according to step ii) can be based on binding assaysdetecting the protein-inhibitor interactions, wherein either thecandidate compound or fungal GTP cyclohydrolase II comprises adetectable label, such as a fluorescent, radioisotopic,chemiluminescent, or enzymatic label, such as horseradish peroxidase,alkaline phosphatase, or luciferase. Detection of a candidate compound,which is bound to the fungal GTP cyclohydrolase II can then beaccomplished, for example, by direct counting of radioemmission, byscintillation counting, or by determining conversion of an appropriatesubstrate to a detectable product.

Preferred examples of these binding assays are fluorescence correlationspectroscopy (FCS) (Proc. Natl. Acad. Sci. USA (1994) 11753-11575),flurescence polarization (Methods in Enzymology 246 (1995), pp. 283-300)or Fluorescence Energy Transfer (FRET) (Cytometry 34, 1998, pp. 159-179;homogeneous Time Resolved Fluorescence (HTRF) is preferred, if FRET isto be used).

Alternatively, binding of a candidate compound to a fungal GTPcyclohydrolase II can be determined without labeling either of theinteractants, e.g. by using a microphysiometer to detect binding of acandidate compound to the fungal GTP cyclohydrolase II. Amicrophysiometer (e.g., Cytosensor™) is an analytical instrument thatmeasures the rate at which a cell acidifies its environment using alight-addressable potentiometric sensor (LAPS). Changes in thisacidification rate can be used as an indicator of the interactionbetween a candidate compound and fungal GTP cyclohydrolase II (accordingto McConnell et al., Science 2.57, 19061912, 1992). In addition,determining the ability of a candidate compound to bind to the fungalGTP cyclohydrolase II can be accomplished using a technology such asreal-time Bimolecular Interaction Analysis (BIA) (Sjolander &Urbaniczky, Anal. Chem. 63, 23382345, 1991, and Szabo et al., Curr.Opin. Struct. Biol. 5, 699705, 1995), a technology for studyingbiospecific interactions in real time, without labeling any of theinteractants (e.g. BIAcore). Changes in the optical phenomenon surfaceplasmone resonance can be used as an indication of real-time reactionsbetween biological molecules. Also surface-enhanced laserdesorption/ionization (SELDI) in combination with a time-of-flight massspectrometer (MALDI-TOF) makes the rapid analysis of molecules on asupport possible and can be used for analyzing protein-ligandinteractions (Worral et al., (1998) Anal. Biochem. 70:750-756).

Alternatively, all of the above-mentioned methods can be based on a“competition assay”, wherein a reference molecule is replaced by thecandidate compound.

It is also possible to detect further potential antifungal agents by“molecular modeling” via elucidation of the three-dimensional structureof the polypeptide according to the invention using x-ray structureanalysis. The preparation of protein crystals required for x-raystructure analysis, and the corresponding measurements and subsequentevaluations of said measurements, as well as the methodology of“molecular modeling” are known to the skilled worker. In principle,optimization via “molecular modeling” of the active ingredientsidentified by the abovementioned methods is also possible.

The selection according to steps iii) and iv) preferably comprisestesting a candidate compound in a fungal GTP cyclohydrolase IIinhibition assay.

By preference, the selection according to step iii), herein afterreferred to as “in vitro assay”, is based on the following steps:

-   -   a) incubating, with a candidate compound, the fungal GTP        cyclohydrolase II in a cell free system;    -   b) selecting, by step b), a candidate compound which decreases        the activity of fungal GTP cyclohydrolase II.

The enzymatic activity of the fungal GTP cyclohydrolase II is preferablydetermined in comparison to the activity of a fungal GTP cyclohydrolaseII not incubated with the candidate compound.

In step (b), candidate compounds are selected which brought about asignificant decrease in the enzymatic activity corresponding to areduction of at least 10%, advantageously at least 20%, preferably atleast 30%, especially preferably by at least 50% and very especiallypreferably by at least 70%, or a 100% reduction (blocking) beingachieved.

Suitable substrates added to the reaction mixture in step b) fordetermination of enzymatic activity are GTP or GTP comprising adetectable label, such as a fluorescent, radioisotopic orchemiluminescent label. These labled derivatives are hereinafterreferred to as “GTP-analogs”.

For determination of enzymatic activity of fungal GTP cyclohydrolase IIin step b) of the in vitro assay, a fungal GTP cyclohydrolase IIcomprising mixture (e.g. crude cell extract, partially or totallypurified protein) is incubated with a suitable substrate and theconversion of the substrate or the increase in the resultant product ismonitored e.g. by HPLC or by measurement of fluorescence, radioactivityor chemiluminescence of the respective sample.

For example, the enzymatic activity can be determined by HPLC asdescribed in Ritz et. al. Journal of Biological Chemistry 2001, 276:22273-22277) or by monitoring radioactivity as described by Foor andBrown (1980, Meth. Enzymol. 66:303-307). For these methods, GTPcyclohydrolase II is preferably partially purified or purified tohomogeneity.

Although there are enzymatic activity assays by which GTP cyclohydrolaseII activity can be determined, there is a constant need for developmentof new methods for determining enzymatic activity that are easy toperform and also suitable for high throughput Screening (HTS).

Surprisingly, it has been found that GTP cyclohydrolase II activity canbe successfully determined in the presence of the enzyme formatedehydrogenase (E.C. 1.2.1.2). In this method, the formic acid formed byGTP cyclohydrolase can be linked to the reduction of NAD by thecombination of both of these enzymes. The level of formate can bedetermined by monitoring the formation of NADH preferaby by spectroscopyas described by Tishkov and Egorov (SU 1271873).

This method is not only suitable for fungal GTP cyclohydrolase II, butalso for plant GTP cyclohydrolase II and GTP cyclohydrolase I [E.C.3.5.4.16], an enzyme having the same substrate specificity as GTPcyclohydrolase I but a different physiological function: GTPcyclohydrolase I that catalyses the first step in the biosynthesis oftetrahydrofolate and tetrahydrobiopterin. Within the scope of thepresent invention, this method is used preferably for fungal GTPcyclohydrolase II.

Thus, the present invention encompasses a method for determination ofGTP cyclohydrolase activity comprising the following steps:

-   -   a) adding GTP or GTP analog, NAD+ and formate dehydrogenase to a        sample comprising a GTP cyclohydrolase II or I; and    -   b) determination of the NADH content.

If the method is used for an inhibition assay, it can comprise thefollowing steps to ensure that the candidate compound inhibits GTPcyclohydrolase II and not formate dehydrogenase:

-   -   a) adding GTP or GTP analog, NAD+ and formate dehydrogenase to a        sample comprising GTP cyclohydrolase I or II;    -   b) adding formate, NAD+ and formate dehydrogenase to a second        sample comprising fungal GTP cyclohydrolase II;    -   c) adding to the sample of step a) and step b) a candidate        compound;    -   d) determining the activity of both samples;    -   e) selecting candidate compounds that show inhibition in the        presence of GTP and no inhibition in the presence of formic        acid.

Thus, in a particularly preferred embodiment, the GTP cyclohydrolase IIactivity in step c) of the in vitro assay is determined in the presenceof the enzyme formate dehydrogenase (E.C. 1.2.1.2) comprising thefollowing steps:

-   -   a) adding GTP or GTP analog, NAD+ and formate dehydrogenase to a        sample comprising fungal GTP cyclohydrolase II; and    -   b) determination of the NADH content.

In another particulary preferred embodiment, the in vitro assaycomprises the following steps:

-   -   a) adding GTP or GTP analog, NAD+ and formate dehydrogenase to a        sample comprising fungal GTP cyclohydrolase II;    -   b) adding formate, NAD+ and formate dehydrogenase to a second        sample comprising fungal GTP cyclohydrolase II;    -   c) adding to the sample of step a) and step b) a candidate        compound;    -   d) determining the activity of both samples;    -   e) selecting candidate compounds that show inhibition in the        presence of GTP and no inhibition in the presence of formic        acid.

This method is suitable even if unpurified cell extracts (lysates) areput in the respective assay. Furthermore, this method is applicable tohigh throughput screening for inhibitors of fungal GTP cyclohydrolaseII. If lysates or enzyme samples are used in which both enzymes, GTPcyclohydrolase I and GTP cyclohydrolase II are present, the selectedcandidate compounds can be optionally further tested in anotherinhibition assay to confirm whether GTP cyclohydrolase I or GTPcyclohydrolase II is inhibited (e.g. according to Ritz et. al. Journalof Biological Chemistry 2001, 276: 22273-22277).

The fungal GTP cyclohydrolase II used for the in vitro test can bepresent in the lysate of the fungi or of the transgenic organismaccording to the invention. If required, the polypeptide according tothe invention can be purified partially or fully by customary methods. Ageneral overview of customary techniques for purification of proteins isgiven, for example, in Ausubel, F. M. et al., Current Protocols inMolecular Biology, Greene Publishing Assoc. and Wiley-Interscience(1994); ISBN 0-87969-309-6. In the case of recombinant production,purification of the protein fused to an affinity tag may be effected byaffinity chromatography.

The fungal GTP cyclohydrolase II used for the above-mentioned in vitroassay can either be expressed in a transgenic organism transformed withan expression cassette comprising a nucleic acid sequence encoding afungal GTP cyclohydrolase II in enzymatically active form or be obtainedby culturing fungi naturally comprising a GTP cyclohydrolase II.

How to perform heterologous expression of an enzyme-like fungal GTPcyclohydrolase II is well known to the skilled artisan. First,appropriate expression cassettes and/or vectors comprising theexpression cassette have to be prepared, or alternatively, commercialavailable vectors can be used. Besides plasmids, vectors are alsounderstood as meaning all the other vectors known to the skilled workersuch as, for example, phages, viruses such as SV40, CMV, baculovirus,adenovirus, transposons, IS elements, phasmids, phagemids, cosmids,linear DNA or circular DNA. These vectors are capable of beingreplicated autonomously in the host organism or replicatedchromosomally, chromosomal replication being preferred.

Suitable expression cassette comprises fungal GTP cyclohydrolase IIencoding nucleic acid sequence operatively linked to control elements,which govern the expression of the coding sequence in the host cell. Inaccordance with a preferred embodiment, an expression cassette accordingto the invention comprises, at the 5′ end of the coding sequence, apromoter and at the 3′ end a transcription/termination signal and, ifappropriate, further genetic control sequences which are linked operablyto the interposed coding sequence of the fungal GTP cyclohydrolase II.

Also suitable are analogs of the above-described expression cassetteswhich can originate, for example, from a combination of the individualnucleic acid sequences on one polynucleotide (multiple constructs), morethan one polynucleotide in a cell (cotransformation), or by sequentialtransformation.

Advantageous control sequences for the expression cassettes or vectorsaccording to the invention are present, for example, in promoters suchas the cos, tac, trp, tet, lpp, lac, lacIq, T7, T5, T3, gal, trc, ara,SP6, l-PR or in the l-PL promoter, all of which can be used forexpressing fungal GTP cyclohydrolase II in Gram-negative bacterialstrains.

Further advantageous control sequences are present for example in thepromoters amy and SPO2, both of which can be used for expressing fungalGTP cyclohydrolase II in Gram-positive bacterial strains, and in theyeast or fungal promoters AUG1-, ADC1 GPD-1-, PX6-, TEF-, CUP1-, PGK-,GAP1-, TPI, PHO5-, AOX1, GAL10/CYC-1, CYC1, OliC-, ADH-, TDH-, Kex2-,MFa-, rp28- or the NMT-promotor or combinations of the aforementionedpromotors (Degryse et al., Yeast 1995 Jun. 15; 11(7):629-40; Romanos etal. Yeast 1992 June; 8(6):423-88; Benito et al. Eur. J. Plant Pathol.104, 207-220 (1998); Cregg et al. Biotechnology (N.Y.) 1993 Aug.;11(8):905-10; Luo X., Gene 1995 Sep. 22; 163(1):127-31; Nacken et al.,Gene 1996 Oct. 10; 175(1-2): 253-60; Turgeon et al., Mol Cell Biol 1987Sep.; 7(9):3297-305) all of which can be used for expressing fungal GTPcyclohydrolase II in yeast strains. Examples of suitable terminators arethe NMT-, Gcy1-, TrpC-, AOX1-, nos-, the PGK- or the CYC1-terminator,preferably the nos-terminator (Degryse et al., Yeast 1995 Jun. 15;11(7):629-40; Brunelli et al. Yeast 1993 Dec. 9(12): 1309-18; Frisch etal., Plant Mol. Biol. 27 (2), 405-409 (1995); Scorer et al.,Biotechnology (N.Y.) 12 (2), 181-184 (1994), Genbank acc. number Z46232;Zhao et al. Genbank acc number: AF049064; Punt et al., (1987) Gene 56(1), 117-124).

Control elements which may be mentioned as being suitable for expressionin insect cells are, for example, the polyhedrin promoter and the p10promoter (Luckow, V. A. and Summers, M. D. (1988) Bio/Techn. 6, 47-55).

Examples of advantageous control sequences for expressing fungal. GTPcyclohydrolase II in cell culture are, besides polyadenylationsequences, the following eukaryotic promoters of viral origin, such as,for example, promoters of the polyoma virus, adenovirus 2,cytomegalovirus or simian virus 40.

Further prokaryotic and eukaryotic expression systems are mentioned inChapters 16 and 17 in Sambrook et al., Molecular Cloning: A LaboratoryManual. 2nd ed., Cold Spring Harbor Laboratory, Cold Spring HarborLaboratory Press, Cold Spring Harbor, N.Y., 1989.

The expression cassettes according to the invention and the vectorsderived from them may also comprise further functional elements, inaddition to the abovementioned promoters. The following may be mentionedby way of example, but not by limitation: reporter genes, origins ofreplication, selection markers and/or affinity tags, fused to fungal GTPcyclohydrolase II either directly or by means of a linker optionallycomprising a protease cleavage site.

The expression cassette and the vectors derived from them can beemployed for the transformation of bacteria, cyanobacteria, yeasts,filamentous fungi and algae and eukaryotic cells (for example insectcells) with the purpose of recombinantly producing fungal GTPcyclohydrolase II, the generation of a suitable expression cassettedepending on the organism in which the gene is to be expressed.

The nucleic acid encoding a fungal GTP cyclohydrolase II mayadvantageously also be introduced into the organisms in the form of alinear DNA and integrated into the genome of the host organism viaheterologous or homologous recombination. This linear DNA may consist ofa linearized plasmid or else only of the nucleic acid construct asvector or the nucleic acid sequences used. In a further advantageousembodiment, the nucleic acid sequences used in the method according tothe invention may also be introduced into an organism by themselves. If,besides the nucleic acid sequences, further genes are to be introducedinto the organism, all the genes may be introduced together into theorganism in a single vector or each individual gene may be introducedinto the organism in one vector each, it being possible to introduce thevarious vectors simultaneously or in succession.

The transgenic organisms generated by transformation can be used forrecombinant expression of fungal GTP cyclohydrolase II.

Other preferred microorganisms for the recombinant expression are,besides bacteria, yeasts and fungi, and eukaryotic cell lines.

Preferred within the bacteria are bacteria of the genus Escherichia,Erwinia, Flavobacterium, Alcaligenes or cyanobacteria, for example ofthe genus Synechocystis or Anabena.

Preferred yeasts are Candida, Saccharomyces, Hansenula or Pichia.

Preferred fungi are Aspergillus, Trichoderma, Ashbya, Neurospora,Fusarium, Beauveria, Mortierella, Saprolegnia, Pythium, or other fungidescribed in Indian Chem Engr. Section B. Vol 37, No 1, 2 (1995).

In principle, transgenic animals are also suitable as host organisms,for example C. elegans.

As aforementioned, also preferred is the use of expression systems andvectors which are publicly accessible or commercially available.

The typical advantageous commercially available fusion and expressionvectors may be mentioned in this context: pGEX [Pharmacia Biotech Inc;Smith, D. B. and Johnson, K. S. (1988) Gene 67:31-40], PMAL (New EnglandBiolabs, Beverly, Mass.) and pRIT5 (Pharmacia, Piscataway, N.J.) whichcomprises glutathion S-transferase (GST), Maltose binding protein, orprotein A, the pTrc vectors (Amann et al., (1988) Gene 69:301-315), the“pKK233-2” from CLONTECH, Palo Alto, Calif. and the “pET” and “pBAD”vector series from Stratagene, La Jolla.

Further advantageous vectors for use in yeast are pYepSec1 (Baldari, etal., (1987) Embo J. 6:229-234), pMFa (Kurjan and Herskowitz, (1982) Cell30:933-943), pJRY88 (Schultz et al., (1987) Gene 54:113-123), and pYESderivatives, GAPZ derivatives, pPICZ derivatives, and the vectors of the“Pichia expression kit” (Invitrogen Corporation, San Diego, Calif.).Vectors for use in filamentous fungi are described in: van den Hondel,C.A.M.J.J. & Punt, P. J. (1991) “Gene transfer systems and vectordevelopment for filamentous fungi, in: Applied Molecular Genetics ofFungi, J. F. Peberdy, et al., eds., p. 1-28, Cambridge University Press:Cambridge.

As an alternative, insect cell expression vectors may also be usedadvantageously, for example for expression in Sf 9 cells. These are forexample the vectors of the pAc series (Smith et al. (1983) Mol. CellBiol. 3:2156-2165) and the pVL series (Lucklow and Summers (1989)Virology 170:31-39). Others which may be mentioned are the baculovirusexpression systems “MaxBac 2.0 kit” from Invitrogen, Carlsbad, or“BacPAK baculovirus expression system” from CLONTECH, Palo Alto, Calif.

Moreover, the fungal GTP cyclohydrolase II can be expressed in mammaliancells. Examples of such expression vectors are pCDM8 and pMT2P, whichare mentioned in: Seed, B. (1987) Nature 329:840 or Kaufman et al.(1987) EMBO J. 6:187-195). In this complex, promoters to be used bypreference are of viral origin such as, for example, promoters ofpolyoma virus, adenovirus 2, cytomegalovirus or simian virus 40. Furtherprokaryotic and eukaryotic expression systems are mentioned in Chapters16 and 17 in Sambrook et al., Molecular Cloning: A Laboratory Manual.2nd ed., Cold Spring Harbor Laboratory, Cold Spring Harbor LaboratoryPress, Cold Spring Harbor, N.Y., 1989.

All above-mentioned organisms transformed with at least one of theabove-mentioned expression cassettes or vectors are herein below termedas “transgenic organism according to the invention”.

The fungal GTP cyclohydrolase II can be isolated from an organismnaturally comprising a fungal GTP cyclohydrolase II, for example fromthe pathogenic fungi mentioned above and for example from fungi selectedfrom the group consisting of the genera and species, e.g. Pichia such asPichia pastoris and Pichia methanolica, Saccharomyces such asSaccharomyces cerevisiae, Hansenula such as Hansenula poymorpha;Trichoderma, Ashbya such as Ashbya gossipii, Neurospora such asNeurospora crassa, Beauveria, Mortierella, Saprolegnia, Pythium, orother fungi described in Indian Chem Engr. Section B. Vol 37, No 1,2(1995).

The selection according to step iv) is based on an in vivo assay. In apreferred embodiment this comprises the following steps:

-   -   a) the generation of a transgenic organism according to the        invention which, following transformation with a nucleic acid        sequence encoding a fungal GTP cyclohydrolase II, is capable of        overexpressing polypeptide with GTP cyclohydrolase II activity;    -   b) the application, to the fungi of step a) and to an analogous,        untransformed fungi, of a candidate compound;    -   c) the determination of the growth, the viability or infectivity        of the transgenic and the untransformed organism following        application of the substance of step b); and    -   d) the selection of candidate compounds, which reduces growth,        viability or infectivity of the transgenic and the untransformed        fungi following application of the substance of step b).

In this step (c), compounds are selected which brought about a reductionin growth, viability or infectivity of at least 10%, advantageously atleast 20%, preferably at least 30%, especially preferably by at least50% and very especially preferably by at least 70%, or a 100% reduction(blocking) being achieved.

An analogous untransformed organism is to be understood as the fungiwhich has been used for generating the transgenic organism according tothe invention in step a).

Suitable organisms are the fungi defined above, preferably those, whichcan be easily genetically manipulated by the skilled artisan, e.g.Saccharomyces species, Pichia species, Fusarium species, Ashbya species,Schizosaccharomyces species, Magnaporte species, Ustilago species,Neurospora species and Klyveromyces species.

When a sample comprising an antifungal agent has been identified by themethod according to the invention, it is either possible to isolate thesubstance directly from the original samples, or else the sample can bedivided into different groups, for example when it consists of amultiplicity of different components, in order to reduce the number ofdifferent substances per sample and then to repeat the method accordingto the invention with such a “subsample” of the original sample.Depending on the complexity of the sample, the above-described steps canbe repeated several times, preferably until the sample identified inaccordance with the method according to the invention only encompasses asmall number of substances or only one substance. The substanceidentified in accordance with the method according to the invention, orderivatives thereof, is preferably formulated further so that it issuitable for use in plant breeding or in plant cell or plant tissueculture.

All of the antifungal agents identified by the abovementioned methodscan subsequently be tested for their fungicidal action in a furtherin-vivo activity test. Here, the substance in question is incubated witha culture of a pathogenic fungus, preferably a culture of aphytopathogenic fungus, especially preferably a culture of a filamentousphytopathogenic fungus, it being possible to determine the fungicidalaction for example on the basis of limited growth.

The above-mentioned embodiments of the method for identifying antifungalagents are preferably realized in a high throughput screening. Usinghigh throughput screening, many discrete compounds can be tested inparallel so that large numbers of candidate compounds can be quicklyscreened.

The most widely established techniques utilize 96-well, 384-well and1536-well microtiter plates. The wells of the microtiter platestypically require assay volumes that range from 50 to 500 μl, preferably200 μl. In addition to the plates, many instruments, materials,pipettors, robotics, plate washers, and plate readers are commerciallyavailable to fit the respective well format.

Alternatively, free format assays or assays that have no physicalbarrier between samples, can be used as described in Jayaickreme et al.(Proc. Natl. Acad. Sci U.S.A. 19 (1994) 161418), Chelsky (“Strategiesfor Screening Combinatorial Libaries”, First Annual Conference of TheSociety for Biomolecular Screening in Philadelphia, Pa. (November 710,1995)) and Salmon et al. (Molecular Diversity 2 (1996), 5763).Additionally, a high throughput screening method as described in U.S.Pat. No. 5,976,813 can be used based on a porous matrix, in which testsamples are placed; one or more assay components are then placed within,on top of, or at the bottom of a matrix such as a gel, a plastic sheet,a filter, or other form of easily manipulated solid support. Whensamples are introduced to the porous matrix they diffuse sufficientlyslowly, such that the assays can be performed without the test samplesrunning together.

It may be desirable for HTS to immobilize either the fungal GTPcyclohydrolase II or the candidate compound to facilitate separation ofbound and unbound forms of one or both of the interactants, as well asto accommodate automation of the assay. Thus, either the fungal GTPcyclohydrolase II or the candidate compound is preferably bound to asolid support. Suitable solid supports include, but are not limited to,glass or plastic slides, tissue culture plates, microtiter wells, tubes,silicon chips, or particles such as beads (including, but not limitedto, latex, polystyrene, or glass beads). Any method known in the art canbe used to attach the fungal GTP cyclohydrolase II or candidate compoundto a solid support, including the use of covalent and non-covalentlinkages, passive absorption, or pairs of binding moieties attachedrespectively to the fungal GTP cyclohydrolase II or candidate compoundand the solid support. Candidate compounds are preferably bound to thesolid support in an array, so that the location of individual candidatecompounds can be tracked. Binding of a candidate compound to a fungalGTP cyclohydrolase II can be accomplished in any vessel suitable forcontaining the reactants. Examples of such vessels include microtiterplates, test tubes, and microcentrifuge tubes.

All of the antifungal agents identified by the abovementioned methodsfurther designated as “identified compounds” are subject matter of thepresent invention. Preferably, they have a molecular weight below 1000g/mol, preferably 500 g/mol, more preferably 400 g/mol and mostpreferably 300 g/mol. The identified compounds further exhibit a Kivalue below 1 mM, preferably 1 μM, more preferably 0.1 μM and mostpreferably 0.01 μM.

The identified compounds may be: expression libraries, for example cDNAexpression libraries, peptides, proteins, nucleic acids, antibodies,small organic substances, hormones, PNA(s) or the like (Milner, NatureMedicine 1 (1995), 879-880; Hupp, Cell. 83 (1995), 237-245; Gibbs, Cell.79 (1994), 193-198 and references cited therein). They may be chemicallysynthesized substances or substances produced by microorganisms and canbe present for example in cell extracts or, for example, plants, animalsor microorganisms. The reaction mixture can be a cell-free extract orcomprise a cell or cell culture. Suitable methods are known to theskilled worker and are described generally for example in Alberts,Molecular Biology the cell, 3^(rd) Edition (1994), for example Chapter17. For example, the substances mentioned can be added to the reactionmixture or the culture medium or injected into the cells or sprayed ontoa plant.

The identified compounds may also be present in the form of theiragriculturally useful salts. Suitable salts among agriculturally usefulsalts are mainly the salts of those cations or the acid addition saltsof those acids whose cations, or anions, respectively, do not adverselyaffect the fungicidal action of the identified compound.

All of the identified compounds—if they comprise asymmetricallysubstituted α-carbon atoms—exist either as racemates, enantiomermixtures or as pure enantiomers and—if they have chiral substituents—mayalso exist as diastereomer mixtures. They are suitable for controllingthe pathogenic fungi mentioned at the outset.

The invention therefore furthermore relates to processes for thepreparation of the fungicidal composition, which comprises

-   -   a) selection of an identified compound; and    -   b) formulating the identified compound, or an agriculturally        useful salt of the identified compound identified via (a), with        suitable adjuvants.

The identified compounds according to the invention in step a) can beformulated for example in the form of directly sprayable aqueoussolutions, powders, suspensions, also highly concentrated aqueous, oilyor other suspensions or suspoemulsions or dispersions, emulsions, oildispersions, pastes, dusts, compositions for spreading, or granules, andapplied by spraying, atomizing, dusting, spreading or pouring. The useforms depend on the intended purposes and the nature of the identifiedcompound used; in any case, they should ensure the finest possibledistribution of the identified compounds according to the invention.

For the preparation of emulsions, pastes or aqueous or oil-containingdispersions, the identified compounds as such can be dissolved ordispersed in an oil or solvent, it being possible to add furtherformulation auxiliaries for homogenization. However, it is also possibleto prepare liquid or solid concentrates which are composed of identifiedcompound and, if appropriate, solvent or oil and optionally furtherauxiliaries, and these concentrates are suitable for dilution withwater. Materials which may be mentioned in this context are emulsionconcentrates (EC, EW), suspensions (SC), soluble concentrates (SL),pastes, pellets, wettable powders or granules, it being possible for thesolid formulations to be either soluble or dispersible (wettable) inwater. Moreover, such powders or granules or tablets may additionally beprovided with a solid coating which prevents abrasion or an unduly earlyrelease of the identified compound.

The term auxiliaries is understood as meaning, in principle, thefollowing classes of substances: antifoams, thickeners, wetters,stickers, dispersants or emulsifiers, bactericides and thixotropicagents. The skilled worked is familiar with the meaning of theabovementioned agents.

SLs, EWs and ECs can be prepared by simply mixing the constituents inquestion; powders can be prepared via mixing or grinding in specifictypes of mills (for example hammer mills). SCs and SEs are usuallyprepared by wet milling, it being possible to prepare an SE from an SCby adding an organic phase comprising further auxiliaries or identifiedcompounds. The preparation is known. Granules, for example coatinggranules, impregnated granules and homogeneous granules, can be preparedby binding the identified compounds to solid carriers. The skilledworker is familiar with a multiplicity of solid carriers which aresuitable for granules according to the invention, for example mineralearths such as silicas, silica gels, silicates, talc, kaolin, limestone,lime, chalk, bole, loess, clay, dolomite, diatomaceous earth, calciumsulfate, magnesium sulfate, magnesium oxide, ground synthetic materials,fertilizers such as ammonium sulfate, ammonium phosphate, ammoniumnitrate, ureas, and products of vegetable origin such as cereal meal,tree bark meal, wood meal and nutshell meal, cellulose powders or othersolid carriers. The skilled worker is familiar with details of thepreparation; they are stated, for example, in the followingpublications: U.S. Pat. No. 3,060,084, EP-A 707445 (for liquidconcentrates), Browning, “Agglomeration”, Chemical Engineering, Dec. 4,1967, 147-48, Perry's Chemical Engineer's Handbook, 4th Ed.,McGraw-Hill, New York, 1963, pages 8-57 and ff. WO 91/13546, U.S. Pat.No. 4,172,714, U.S. Pat. No. 4,144,050, U.S. Pat. No. 3,920,442, U.S.Pat. No. 5,180,587, U.S. Pat. No. 5,232,701, U.S. Pat. No. 5,208,030, GB2,095,558, U.S. Pat. No. 3,299,566, Klingman, Weed Control as a Science,John Wiley and Sons, Inc., New York, 1961, Hance et al., Weed ControlHandbook, 8th Ed., Blackwell Scientific Publications, Oxford, 1989, andMollet, H., Grubemann, A., Formulation technology, Wiley VCH VerlagGmbH, Weinheim (Federal Republic of Germany), 2001.

The skilled worker is familiar with a multiplicity of inert liquidand/or solid carriers which are suitable for the formulations accordingto the invention, such as, for example, liquid additives such as mineraloil fractions of medium to high boiling point, such as kerosene ordiesel oil, furthermore coal tar oils and oils of vegetable or animalorigin, aliphatic, cyclic and aromatic hydrocarbons, for exampleparaffin, tetrahydronaphthalene, alkylated naphthalenes or theirderivatives, alkylated benzenes or their derivatives, alcohols such asmethanol, ethanol, propanol, butanol, cyclohexanol, ketones such ascyclohexanone, or strongly polar solvents, for example amines such asN-methyl-pyrrolidone, or water.

The skilled worker is familiar with a multiplicity of surface-activesubstances (surfactants) which are suitable for the formulationsaccording to the invention, such as, for example, the alkali, alkalineearth or ammonium salts of aromatic sulfonic acids, for example ligninsulfonic acid, phenol sulfonic acid, naphthalene sulfonic acid anddibutylnaphthalenesulfonic acid, and of fatty acids, alkyl sulfonates,alkylaryl sulfonates, alkyl sulfates, lauryl ether sulfates and fattyalcohol sulfates, and salts of sulfated hexadecanols, heptadecanols andoctadecanols, and of fatty alcohol glycol ethers; condensates ofsulfonated naphthalene and its derivatives with formaldehyde,condensates of naphthalene or of the naphthalene sulfonic acids withphenol and formaldehyde, polyoxyethylene octylphenol ether, ethoxylatediso-octylphenol, octylphenol or nonylphenol, alkylphenyl ortributylphenyl polyglycol ether, alkylaryl polyether alcohols,isotridecyl alcohol, fatty alcohol/ethylene oxide condensates,ethoxylated castor oil, polyoxyethylene alkyl ethers orpolyoxypropylenealkyl ethers, lauryl alcohol polyglycol ether acetate,sorbitol esters, lignin-sulfite waste liquors or methylcellulose.

Powders, dusts and materials for spreading, being solid carriers, can beprepared advantageously by mixing or concomitantly grinding the activesubstances with a solid carrier.

The concentrations of the identified compounds in the ready-to-usepreparations can be varied within wide limits and depend on the natureof the formulation in question.

The fungicidal compositions, or the identified compounds, can be appliedin curative.

The applications of identified compounds (=substances and/orcompositions) amount to from 0.001 to 3.0, preferably 0.01 to 1.0 kg/haactive substance, depending on the aim of the control measures, theseason, the target plants and the stage of growth.

The present invention furthermore relates to a method of controllingharmful fungi, which comprises treating the fungi or the materials,plants, soils or seeds to be protected from fungal infection, with aneffective amount of an antifungal agent according to the invention or ofa fungicidal composition according to the invention. Harmful fungi areunderstood as meaning the pathogenic fungi mentioned at the outset.

Another object of the present invention is the use of the identifiedcompounds for preparation of drugs, preferably pharmaceuticalcompositions comprising at least an identified compound. The identifiedcompounds according to the invention can be administered orally orparenterally (subcutaneously, intravenously, intramuscularly andintraperitoneally) in a conventional way. Administration may also takeplace with vapors or sprays through the nasopharyngeal space.

The dosage depends on the age, condition and weight of the patient andon the mode of administration. As a rule, the daily dose of activesubstance is about 0.5-50 mg/kg of bodyweight on oral administration andabout 0.1-10 mg/kg of bodyweight on parenteral administration.

The identified compounds can be used in conventional solid or liquidpharmaceutical forms, eg. as uncoated or (film-)coated tablets,capsules, powders, granules, suppositories, solutions, ointments, creamsor sprays. These are produced in a conventional way. For this purpose,the active substances can be processed with conventional pharmaceuticalexcipients such as tablet binders, bulking agents, preservatives, tabletdisintegrants, flow regulators, plasticizers, wetting agents,dispersants, emulsifiers, solvents, release-slowing agents, antioxidantsand/or propellant gases (cf. H. Sucker et al.: PharmazeutischeTechnologie, Thieme-Verlag, Stuttgart, 1991). The administration formsobtained in this way normally contain from 0.1 to 90% by weight ofactive substance.

The invention is now illustrated by the examples which follow, but arenot limited thereto.

The recombinant methods on which the exemplary embodiments which followare based are now described briefly:

A: General Methods

Cloning methods such as, for example, restriction cleavages, DNAisolation, agarose gel electrophoresis, purification of DNA fragments,transfer of nucleic acids to nitrocellulose and nylon membranes, linkingof DNA fragments, transformation of E. coli cells, bacterial cultures,sequence analysis of recombinant DNA and Southern and Western Blots werecarried out as described by Sambrook et al., Cold Spring HarborLaboratory Press (1989) and Ausubel, F. M. et al., Current Protocols inMolecular Biology, Greene Publishing Assoc. and Wiley-Interscience(1994); ISBN 0-87969-309-6.

The bacterial strains used hereinbelow (E. coli XL1-blue) were obtainedfrom BRL Gibco or Invitrogen, Carlsberg, Calif. The Ashbya gossypiiwild-type strain has the ATTC number ATTC 10895.

B: Sequence Analysis of Recombinant DNA

Recombinant DNA molecules were sequenced using an ABI laser fluorescenceDNA sequencer following the method of Sanger (Sanger et al., Proc. Natl.Acad. Sci. USA, 74, 5463-5467(1977)). Fragments resulting from apolymerase chain reaction were sequenced and verified in order to avoidpolymerase errors in constructs to be expressed.

C: Materials Used

Unless otherwise specified in the text, all of the chemicals used wereobtained in analytical grade quality from Fluka (Neu-Ulm), Merck(Darmstadt), Roth (Karlsruhe), Serva (Heidelberg) and Sigma(Deisenhofen). Solutions were prepared using pure pyrogen-free water,referred to in the following text as H₂O, from a Milli-Q water systempurification unit (Millipore, Eschborn). Restriction enzymes,DNA-modifying enzymes and molecular-biological kits were obtained fromAGS (Heidelberg), Amersham (Brunswick), Biometra (Göttingen), Roche(Mannheim), Genomed (Bad Oeynnhausen), New England Biolabs(Schwalbach/Taunus), Novagen (Madison, Wis., USA), Perkin-Elmer(Weiterstadt), Pharmacia (Freiburg), Qiagen (Hilden) and Stratagene(Heidelberg). Unless otherwise specified, they were used following themanufacturer's instructions.

All of the media and buffers used for the genetic engineeringexperiments were sterilized either by filter sterilization or by heatingin the autoclave.

EXAMPLE 1

A) Preparation of the Knock-Out Plasmid

The KO plasmid pDeltarib1G418 was obtained from pJR765 (WO95/26406) byinserting the G418R expression cassette (Degryse et al., Yeast 1995,11(7):629-40) into pJR765 so that the GTP cyclohydrolase II gene (rib 1)that is set forth in SEQ ID NO:3 is deleted from 220 bp upstream the ATGcodon to 739 bp downstream the ATG codon. 6 mg plasmid DNA ofpDeltarib1G418 were linearized with the restriction enzyme Asp 700 andpurified by classical gel elution for subsequent transformation.

B) Transformation of Asbya goosypii

A. goosypii spores were cultured for 12 h in MA2 medium (peptone 10 g/l,yeast extract 1 g/l, myoinositol 0.3 g/l, pH7) at 28° C. and 250 rpm.The cells were pelleted by classical centrifugation and suspended withphosphate buffer 50 mM, DTT 25 mM and incubated at 28° C. with lowagitation for 30 min. The cells were collected by centrifugation andsuspended with 25 ml cold phosphate buffer 50 mM pH 7.5; 150 μl of thecell suspension were mixed with 6 μg pDeltarib1 G418 treated with Asp700. The mixture was electroporated with a Gene Pulser II electroporator(Bio-Rad; parameters: 200 ohms; 1.5 Kv; 25 μF)

Immediately after the electric pulse, the cells were mixed with 1 ml MA2medium and spread on fresh Petri dishes containing MA2-agar supplementedwith 200 mg vitamin b2. The plates were incubated at 28° C. for 6 h.Then, a fine layer of Top-agar (1% LMP agarose) containing G418antibiotic 50 mg/ml was loaded at the top of the plates. The incubationwas further conducted at 28° C. for 5 days. Several colonies capable ofgrowth on selective medium were isolated for subsequentcharacterization.

C) Characterization of the KO Mutants

The KO mutants were grown on Petri dishes containing MA2 agar, G418 50mg/ml and vitamin b2 200 mg/ml and then replicated on the same medium inthe absence of vitamin b2. In the latter case, the KO mutants were notable to grow at all. This convincingly demonstrates that GTPcyclohydrolase II is essential for the life of the fungi.

EXAMPLE 2

A) Enzyme Preparation:

Ashbya gossypii cells may be obtained after 2 days from a culture in 3%(w/v) malt extract +0.3% (w/v) difco-soyton, pH 5.6 at 28° C. Acell-free extract can be obtained by mechanical breakage of the cellswith a kitchen blender in 50 mM imidazole buffer pH 7 containing 1 mMEDTA-Na salt, 5 mM MgSO4, 10 mM KCl, 5 mM dithiothreitol and 30% (v/v)glycerol and separation of unbroken cells and debris by centrifugation.

B) Activity Assay

The assay is performed in a suitable buffer e.g. Tris/HCl, pH 7.8including 1 mM Mg.Cl₂, 1 mM DTT, 0.5 mM NAD, 2 units/ml formatedehydrogenase and 2.5 mM GTP Li salt. After the addition of the GTPcyclohydrolase comprising cell free extracts of step A), the reactionwas monitored by measuring the absorption at 340 nm.

After dissolving the respective candidate compounds in a suitablesolvent e.g. DMSO, an aliquot of the afore made solution is added to thereaction mixture. The enzyme activity of this sample is compared withthe activity of a control comprising the pure solvent instead of thecandidate compound. The resulting relative activity was calculated aspercent inhibition in relation to the sample without the candidatecompound.

In FIG. 1, the GTP dependant formation of NADH in the reaction mixtureand inhibition by3-Butyl-10-(3-chlorophenyl)-10H-pyrimido[4,5-b]quinoline-2,4-dione isshown.

To distinguish between the inhibition of GTP cyclohydrolase and formatedehydrogenase in the above-mentioned assay, the subtrate GTP is replacedwith formic acid. An inhibitor of GTP cyclohydrolase shows inhibition inthe presence of GTP and no inhibition in the presence of formic acid(see e.g. FIG. 2).

c) Determination of Fungicidal Activity of3-butyl-10-(3-chlorophenyl)-10H-pyrimido[4,5-b]quinoline-2,4-dione

A stock solution of3-butyl-10-(3-chlorophenyl)-10H-pyrimido[4,5-b]quinoline-2,4-dione isprepared in DMSO at a concentration of 10,000 ppm a.i. For the test,this is diluted with sterile deionized water to a concentration of 125ppm; the DMSO concentration is constant at all test concentrations.

Spore suspensions of the fungi employed in the test (Phytophthorainfestans, Pyricularia oryzae and Septoria tritici) are made in doublestrength growth medium (4% (w/v) malt extract in water).

For each fungal species, 3 (three) wells are prepared: 50 μl of compoundsolution are pipetted to each well, were to this are added 50 μl ofspore suspension. A water/DMSO blank serves as the 100% growth control(=0 ppm); a well without added fungal inoculum but with the growthmedium serves as medium blank.

The prepared plates are then incubated at 18° C. for 7 days after whichthe density of developed fungal mycelium is measured in a photometer ata wavelength of 405 nm.

After subtracting the medium blank readings and setting, the 100% growthcontrol reading, the measurements from the concentration series areconverted into “% growth compared with the 0 ppm control”. The data setforth in table 1 clearly show that fungal growth was significantlyinhibited by3-butyl-10-(3-chlorophenyl)-10H-pyrimido[4,5-b]quinoline-2,4-dione.

TABLE 1 Pyricularia oryzae*) Phytophthora infestans*) Septoria tritici*)47.6% 39.9% 0% *)[% growth compared with the 0 ppm control]

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows the GTP dependent formation of NADH in the reaction mixtureand inhibition by3-butyl-10-(3-chlorophenyl)-10H-pyrimido[4,5-b]quinoline-2,4-dione. Inthis figure, ♦ designates values measured in the presence of GTP, ▪values measured without GTP and ▴ values measured in the presence of GTPand 3-butyl-10-(3-chlorophenyl)-10H-pyrimido[4,5-b]quinoline-2,4-dione.

FIG. 2 shows the specificity of the inhibition by3-butyl-10-(3-chlorophenyl)-10H-pyrimido[4,5-b]quinoline-2,4-dione. Noinhibition of formate dehydrogenase alone is observed. Therefore, theinhibition of the GTP dependent NADH formation is a consequence of theinhibition of GTP cyclohydrolase. In this figure, ♦ designates valuesmeasured in the presence of formate, ▪ values measured without formateand ★ values measured in the presence of formate and3-butyl-10-(3-chlorophenyl)-10H-pyrimido[4,5-b]quinoline-2,4-dione.

1. A method for identification of a candidate compound as an inhibitorof GTP cyclohydrolase I or II comprising the steps of: a) adding GTP orGTP analog, NAD+ and formate dehydrogenase to a first sample comprisingGTP cyclohydrolase I or II; b) adding formate, NAD+ and formatedehydrogenase to a second sample comprising GTP cyclohydrolase I or II;c) adding to the first sample and to the second sample, a candidatecompound; d) determining the production of NADH in the first sample andthe second sample, and e) selecting the candidate compound that showsinhibition of NADH production in the presence of GTP and no inhibitionof NADH production in the presence of formate, wherein inhibition ofNADH production in the first sample and no inhibition of NADH productionin the second sample identifies that the candidate compound is aninhibitor of GTP cyclohydrolase I or II and not an inhibitor of formatedehydrogenase.
 2. The method of claim 1, wherein GTP is used assubstrate for the GTP cyclohydrolase and the production of NADH isdetermined by monitoring an increase in absorption at 340 nm.
 3. Themethod of claim 1, wherein the identification of an inhibitor of GTPcyclohydrolase I or II is by high-throughput screening.